1. Field of the Invention
The present invention relates to a laser processing apparatus for applying a pulsed laser beam to a workpiece to laser-process the workpiece.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby partition a plurality of bands where devices such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the streets to thereby divide the bands where the devices are formed from each other, thus obtaining individual semiconductor chips. Further, an optical device wafer is provided by forming photodetectors such as photodiodes or light emitting devices such as laser diodes on the front side of a sapphire substrate. The optical device wafer is also cut along the streets to obtain individual optical devices divided from each other, such as photodiodes and laser diodes, which are widely used in electric equipment.
As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the streets, there has been proposed a method including the steps of applying a pulsed laser beam to the wafer along the streets to thereby form laser processed grooves on the wafer or modified layers inside the wafer along the streets and next breaking the wafer along the laser processed grooves or the modified layers. A laser processing apparatus for laser-processing a workpiece such as a wafer includes a chuck table for holding the workpiece and pulsed laser beam applying means for applying a pulsed laser beam to the workpiece held on the chuck table. The pulsed laser beam applying means includes a pulsed laser beam oscillator for oscillating a pulsed laser beam, focusing means for focusing the pulsed laser beam oscillated by the pulsed laser beam oscillator and applying this pulsed laser beam focused to the workpiece held on the chuck table, and optical transmitting means for transmitting the pulsed laser beam oscillated by the pulsed laser beam oscillator to the focusing means.
In general, the optical transmitting means for transmitting the pulsed laser beam oscillated by the pulsed laser beam oscillator to the focusing means is provided by an optical system composed of a lens and a mirror. However, the optical system composed of a lens and a mirror has a problem such that the flexibility of design is low, depending on a set position. To solve this problem, optical transmitting means using an optical fiber has been proposed (see Japanese Patent Laid-open No. Hei 5-277775, for example).